Depending on your current animal companion the spell has the following effect:
Boar: You mount up on your boar and get to 105 stamina for 4 seconds. Afterwards you get your old stamina back + 20? bonus stamina.
Snake: Your snake jumps at your target and coils around its legs, stunning it briefly and applying a poison. This also decreases your target's resistance to earth damage by 15% for 6 seconds.
Hawk: Your hawk flies out and attaches itself onto the target's head, dealing 3 ticks of damage over 3 seconds. The third tick will also reduce the target's physical damage resistance for 7 seconds.